Passive evaporative cooling of Historical building
Published on 12 June 2019
Malta
George Refalo
Executive Secretary
About this good practice
Systems installed:
-Indirect cooling. 2 chilled water circuits serve cooling coils installed in the roof ridge. The rising warm air passes over and through the coils resulting in a down draught of cooled air. The copper coils are inclined at ap. 70° to encourage airflow through the coils, and 300mm wide purpose-made trays were installed to collect condensate. The cooling coils call for chilled water in response to variations of both internal temperature and internal relative humidity.When the coils are switched on, the actuators at high level and the dampers at low level will both be set to the minimum aperture.
-Direct cooling. The PDEC system relies on hydraulic nozzles. The air is moisturized by the micronisers situated at the ridge. The downdraught process drives the airflow pattern inside the building avoiding the need for fans, ductwork and suspended ceiling.
-Heating.Fan coils supplied by the heat pump are used for heating. The water temperature in the pump is maximum 50°C. , the peak demand is about 25-30kW to heat the central space from a low ambient temperature of 8°C in winter to 21°C. 2 circuits run from the header along each side of the walkway.
-Automatic ventilation openings. High-level window vents in the ridge of the roof and low level vents on the lower ground floor mounted in the east, west and south walls provide ventilation if opened.
-Night time convective ventilation (passive night cooling) comes into operation when the external temperature
-Indirect cooling. 2 chilled water circuits serve cooling coils installed in the roof ridge. The rising warm air passes over and through the coils resulting in a down draught of cooled air. The copper coils are inclined at ap. 70° to encourage airflow through the coils, and 300mm wide purpose-made trays were installed to collect condensate. The cooling coils call for chilled water in response to variations of both internal temperature and internal relative humidity.When the coils are switched on, the actuators at high level and the dampers at low level will both be set to the minimum aperture.
-Direct cooling. The PDEC system relies on hydraulic nozzles. The air is moisturized by the micronisers situated at the ridge. The downdraught process drives the airflow pattern inside the building avoiding the need for fans, ductwork and suspended ceiling.
-Heating.Fan coils supplied by the heat pump are used for heating. The water temperature in the pump is maximum 50°C. , the peak demand is about 25-30kW to heat the central space from a low ambient temperature of 8°C in winter to 21°C. 2 circuits run from the header along each side of the walkway.
-Automatic ventilation openings. High-level window vents in the ridge of the roof and low level vents on the lower ground floor mounted in the east, west and south walls provide ventilation if opened.
-Night time convective ventilation (passive night cooling) comes into operation when the external temperature
Resources needed
The total cost of the refurbishment and renovation of the building is 4.6 million euro, financed by the Malta Stock Exchange.
Evidence of success
The potential savings for the atrium space represent over 60% of the predicted energy consumption for large fan coil units. The building improvements also reduces the energy consumption of the cassette units by ap. 23%. The total cooling energy consumption using fan coils was estimated at ap.103,924 kWh, compared to 54,139 kWh for the built solution using cooling coils and PDEC, resulting in a total energy saving of 48%. It represents an annual savings of £ 3,080/year based on £ 0.06/kWh.
Potential for learning or transfer
The downdraught process drives the airflow pattern inside the building avoiding the need for fans, ductwork and suspended ceilings. Downdraught cooling and night-time convective cooling strategies have therefore clear benefits in the increased energy efficiency of the building and in the comfort perception by its occupants. Adequate time must be allowed for commissioning and demonstration of the control strategies. The success of Passive Downdraught Evaporative Cooling (PDEC) applied to the central atrium space within the New Stock Exchange in Malta demonstrates the scope for replication throughout Southern Europe, both on new buildings and in refurbishment projects.
Further information
Website
Good practice owner
Organisation
Malta Stock Exchange
Malta
Malta
Contact
George Refalo
Executive Secretary